The present invention relates generally to grain drying equipment and more particularly to an improved continuous flow grain dryer.
It is generally believed that continuous flow dryers, that is, those dryers which have wet grain continually entering the dryer and dried grain continually exiting the dryer, were not suitable for drying grains having a high moisture content. The reason for the difficulties experienced in the use of conventional continuous flow dryers was that they only operated at their optimum design performance over a fairly narrow band of moisture removal range due to fixed design conditions such as a fixed cooling air flow, a fixed cooling plenum exhaust area, a fixed heated air flow and a fixed heat plenum exhaust area.
At a grain moisture removal of 6 to 8 percentage points, most conventional dryers work very well. The cooling rate is matched fairly well with the drying rate. The grain column is usually split 25-35 percent cooling and 65-75 percent heating. The total blower horsepower is normally split to be 30-40 percent cooling and 60-70 percent drying. Dryers with a 25 percent cooling column usually use the upper extreme in cooling horsepower, thus operating the cooling plenum at a higher static pressure than the heating plenum and delivering 50-100 percent more cool air per bushel than drying air.
Under conditions wherein grain coming from the field is very high in moisture, and the drying rate is slowed significantly, the grain in such prior art systems was over cooled, which is not a particular problem from the standpoint of the quality of the grain dried, but it does waste considerable energy. Under very dry grain inlet conditions wherein the moisture removal is in the 3-5 percentage range, cooling is inadequate. If grain conditioned by such a process is to be stored in a non-aerated storage and therefore had to be cooled considerably after being dried in the dryer, the only reasonable solution was believed to be to cut back on the drying temperature to drastically slow down the drying rate to the point at which the grain retention time in the cooling zone was adequate to cool the grain. It is of course well known that the grain to be stored in non-aerated storage cannot be too hot or it will deteriorate. There is, therefore, the need for a continuous flow drying apparatus which will overcome these problems found with prior art devices.
Another weakness with most conventional continuous flow column grain drying devices is that the moisture is monitored near the base of the drying column. Consequently, the flow of grain would not be varied if wetter or drier grain is to suddenly be introduced into the dryer, until such time that this wetter or drier grain reached the point of the monitoring sensor. There is, therefore, a need for equipment of this type which will adequately compensate for this situation of having grain of variable moisture entering the dryer.